1. Field of the Invention
The present invention relates to a valve timing control device, which modifies an open/close timing of an intake valve or an exhaust valve of an internal combustion engine (hereafter, referred as an engine).
2. Description of the Prior Art
Different kinds of devices are known as the conventional valve timing control devices (hereafter, referred as a VVT). FIG. 1 is a lateral cross sectional view showing an internal construction of the conventional VVT disclosed in JP-A-1998/159515. FIG. 2 is a longitudinal cross sectional view taken along lines A1xe2x80x94A1 of FIG. 1. FIG. 3 is an enlarged cross sectional view taken along lines A2xe2x80x94A2 of FIG. 1, showing a tier control member locking a free rotation of two rotational members. FIG. 4A is an enlarged cross sectional view taken along lines A2xe2x80x94A2 of FIG. 1, showing the tier control member releasing the lock of the free rotation due to a release hydraulic pressure supplied from an advance side hydraulic pressure chamber. FIG. 4B is a plane view showing an area of a force-exerted face of the tier control member shown in FIG. 4A. FIG. 5A is an enlarged cross sectional view taken along lines A2xe2x80x94A2 of FIG. 1, showing the tier control member releasing the lock of the free rotation due to a release hydraulic pressure supplied from a retardation side hydraulic pressure chamber. FIG. 5B is a plane view showing an area of a force-exerted face of the tier control member in FIG. 5A.
In the drawings, reference numeral 1 denotes a housing (first rotor) provided integrally a chain sprocket section 1a on which a rotational driving force of a crankshaft (not shown) of the engine. Numeral 2 denotes a case (first rotor) having a plurality of shoes 2a, 2b, 2c and 2d, which is located at the housing 1, and which is projected inwardly to form a plurality of hydraulic pressure chambers. Numeral 3 denotes a rotor (second rotor) including a boss section 3a located at a central part of the rotor 3 and a plurality of vanes 3b, 3c, 3d and 3e formed at an outer peripheral surface of the boss section 3a. The boss section 3a is fixed at an end of a camshaft (not shown) with a bolt (not shown). The vanes 3b, 3c, 3d and 3e partition the plural hydraulic pressure chambers into advance side hydraulic pressure chambers 4 and retardation side hydraulic pressure chambers 5. The advance side hydraulic pressure chamber 4 moves rotationally the second rotor with respect to the first rotor toward the advance side when a hydraulic pressure is supplied from an oil pump (not shown) of the engine via an oil control valve (not shown and hereafter referred as OCV). The retardation side hydraulic pressure chamber 5 moves rotationally the second rotor with respect to the first rotor toward the retardation side when the hydraulic pressure is supplied from the oil pun (not shown) via the OCV. A direction, which is indicated by arrow X1 in FIG. 1, incidentally means a rotational direction of the camshaft (not shown).
Seal members 6 are disposed at ends of the shoes 2a, 2b, 2c and 2d of the case 2 and at ends of the vanes 3b, 3c, 3d and 3e of the rotor 3, respectively. The seal member 6 creates a seal to block flow of actuating oil between the advance side hydraulic pressure chamber 4 and the retardation side hydraulic pressure chamber 5 to keep a hydraulic pressure in the respective hydraulic pressure chambers 4 and 5. The seal member 6 includes a resilient seal 6a made of resin, and a leaf spring 6b, which biases the seal 6a against a seal-facing surface. The seal-facing surface means the outer region of the rotor 3 when the seal 6 is disposed at the case 2, and means an inner region of the case 2 when the seal 6 is disposed at the rotor 3, for example.
Numeral 7 denotes a cover (first rotor) closing an end of the rotor 3, which opposes to the housing 1. The cover 7 is integrally fixed at the housing 1 with a threaded bolt 8 passing through the shoes 2a, 2b, 2c and 2d of the case 2. The housing 1, the case 2 and the cover 7 constitutes the first rotor rotating in synchronization with the crankshaft (not shown).
A locative relationship between the first and second rotors is kept due to the adequate hydraulic pressure supplied to the advance side hydraulic pressure chamber 4 or the retardation side hydraulic pressure chamber 5 when the engine is usually operated. However, when the engine is stopped and a hydraulic pressure in the VVT is returned to an oil pan (not shown), the locative relationship between the first and second rotors is not kept due to the hydraulic pressure. Here, a beat noise (abnormal noise) results when the first rotor comes into contact with and separates from the second rotor over and over again as the engine is restarted. A lock pin (tier control member) 9 is arranged at the VVT in order to prevent the occurrence of the beat noise. The lock pin 9 locks a relative rotation of the first and second rotors when the engine is stopped or restarted, and allows the relative rotation when the engine is usually operated.
The lock pin 9 includes a front minor diameter section 9a, a central flange section 9b, a rear major diameter section 9c and a hollow section 9d as shown in FIG. 2 to FIG. 5B. The central flange section 9b has a diameter being larger than the front minor diameter section 9a, the rear major diameter section 9c has a diameter being larger than the central flange section 9b. The hollow section 9d is formed at a central portion of a bottom of the rear major diameter section 9c. The lock pin 9 is enclosed in an accommodation hole 10, which is formed at the vane 3b of the rotor 3 in an axial direction (directions indicated by arrows Y1 and Y2) of the VVT. A cylindrical holder 11 is press-fitted in the accommodation hole 10 before accommodating the lock pin 9. The holder 11 includes a minor diameter section 11a, a major diameter section 11b and a tier section 11c defined as a boundary between the minor and major diameter sections 11a and 11b. The minor diameter section 11a has an inner diameter corresponding to the outer diameter of central flange section 9b of the lock pin 9. The major diameter section 11b has an inner diameter corresponding to the outer diameter of the rear major diameter section 9c of the lock pin 9. A coil spring (biasing member) 12 is arranged between the bottom of the accommodation hole 10 and the hollow section 9d of the lock pin 9, and biases the lock pin 9 toward the housing 1 at all times. On the other hand, a fitting hole 13 is disposed at an end of the housing 1 facing to the rotor in the axial direction of the VVT, and allows fitting of the front minor diameter section 9a of the lock pin 9. A first release hydraulic pressure chamber 14 is defined between the fitting hole 13 and the front minor diameter section 9a of the lock pin 9, and communicates with the advance side hydraulic pressure chamber 4 at all times. The first release hydraulic pressure chamber 4 does not communicate with the retardation side hydraulic pressure chamber 5 due to the seal member 6. A second release hydraulic pressure chamber 16 is defined between the rear major diameter section 9c of the lock pin 9 and the minor diameter 11a of the holder 11 within the accommodation hole 10. The second release hydraulic pressure chamber 16 communicates with only the retardation side hydraulic pressure chamber 5 at all times via a retardation side communication passage 15.
When the lock pin 9 moves backward due to the release hydraulic pressure, a rear space of the lock pin 9 defined in the accommodation hole 10 functions as a backward pressure chamber. A discharge hole 17 is formed at a rear portion of the accommodation hole 10 as shown in FIG. 2, and discharges the backward pressure to the outside of the VVT. A first oil passage 18 is disposed at the advance side hydraulic pressure chamber 4, and supplies a hydraulic pressure from the OCV (not shown) to the advance side hydraulic pressure chamber 4. A second oil passage 19 is disposed at the retardation side hydraulic pressure chamber 5, and supplies a hydraulic pressure from the OCV (not shown) to the retardation side hydraulic pressure chamber 5.
An operation will be hereafter explained.
When the engine is stopped, oil of the VVT returns to the oil pan (not shown). As shown in FIG. 3, the release hydraulic pressure is not supplied to any of the first release hydraulic pressure chamber 14 and the second release hydraulic pressure chamber 16. The lock pin 9 therefore moves forward (upward of FIG. 3) due to a biasing force of the coil spring 12, and then the front minor diameter section 9a of the lock pin 9 fits in the fitting hole 13. In this way, the relative rotation of the first and second rotors is locked.
The hydraulic pressure of the advance side hydraulic pressure chamber 4 or the retardation side hydraulic pressure chamber 5 is used as the release hydraulic pressure when the engine is usually operated. First, the hydraulic pressure of the advance side hydraulic pressure chamber 4 is used as the release hydraulic pressure. Here, oil is supplied from the oil pump (not shown) to the advance side hydraulic pressure chamber 4 via the OCV (not shown) and the first oil passage 18. The hydraulic pressure of the advance side hydraulic pressure chamber 4 is supplied to the first release hydraulic pressure chamber 14 via a passage defined at the end of the rotor 3 facing to the housing 1 as indicated by arrow of FIG. 4A. The release hydraulic pressure exerts on both ends of the front minor diameter section 9a and the central flange section 9b of the lock pin 9. The lock pin 9 therefore moves backward the accommodation hole 10 as shown in FIG. 4B. The front minor diameter section 9a of the lock pin 9 is finally disconnected from the accommodation hole 10 to allow the relative rotation of the first and second rotors.
The hydraulic pressure of the retardation side hydraulic pressure chamber 5 is used as the release hydraulic pressure. Here, oil is supplied from the oil pump (not shown) to the retardation side hydraulic pressure chamber 5 via the OCV (not shown) and the second oil passage 19. The hydraulic pressure of the retardation side hydraulic pressure chamber 5 is supplied to the second release hydraulic pressure chamber 16 via the retardation side communication passage 15 as indicated by arrow of FIG. 5A. The release hydraulic pressure exerts on the end of the rear major diameter section 9c of the lock pin 9. The lock pin 9 therefore moves backward the accommodation hole 10 as shown in FIG. 5B. The front minor diameter section 9a of the lock pin 9 is finally disconnected from the accommodation hole 10 to allow the relative rotation of the first and second rotors.
The constitution of the conventional VVT above reduces the force-exerted face of the lock pin 9 by half in the two cases of using the release hydraulic pressure of the advance side and using the release hydraulic pressure of the retardation side. In any of these cases, the area of force-exerted face of the lock pin 9 becomes small. It is therefore necessary to set a small biasing force of the coil spring 12 allowing the release due to a small release hydraulic pressure, which exerts on a small area of force-exerted face above. Here, the biasing force of the coil spring 12 and the release hydraulic pressure are both small, and the lock/release operation is therefore susceptible to a sliding resistance of the lock pin 9. When the lock pin 9 is upsized, the sliding resistance can have little effect on the lock/release operation, because the biasing force of coil spring and release hydraulic pressure become both large. The upsizing of the lock pin 9 results in the upsizing of the VVT itself. This runs counter to a downsizing in demand for the VVT in recent years.
The lock pin 9 itself of the conventional VVT is downsized and the biasing force of the coil spring 12 lets it go. In this case, the area of force-exerted face of the lock pin 9 subject to the release hydraulic pressure supplied from the advance side hydraulic pressure chamber 4 becomes small in proportional to the square of the radius of the lock pin 9. The release hydraulic pressure supplied from the advance side hydraulic pressure chamber 4 becomes weak in comparison to the biasing force of the coil spring 12. In this way, the lock pin 9 is resistant to disconnect from the fitting hole 13 when the second rotor locates at an advance side with respect to the first rotor, and the operation of the VVT becomes unstable.
Accordingly, it is an object of the present invention to provide a valve timing control device having the enlarged force-exerted face of the tier control member to ensure the high stability of operation.
In order to achieve the object of the present invention, a valve timing control device comprises a first rotor rotating in synchronization with a crankshaft of an internal combustion engine and having a plurality of shoes which are projected inwardly to define a plurality of hydraulic pressure chambers; a second rotor fixed at an end of a camshaft of the internal combustion engine and having a plurality of vanes which partition the plural hydraulic pressure chambers of the first rotor into an advance side hydraulic pressure chamber and a retardation side hydraulic pressure chamber; a fitting hole disposed at any one of the first rotor or the second rotor; a tier control member fitting in the fitting hole to control a relative rotation of the first and second rotors and having a front minor diameter section and a rear major diameter section; an accommodation hole disposed at the other to accommodate the tier control member; a biasing member biasing the tier control member in a direction of fitting the tier control member in the fitting hole; a first release hydraulic pressure chamber defined between the front minor diameter section of the tier control member and the fitting hole; and a second release hydraulic pressure chamber defined between an end face of the rear major diameter section of the tier control member in an axial direction of the device and the accommodation hole, wherein at least one of the first and second release hydraulic pressure chambers communicates with both the advance and retardation side hydraulic pressure chambers. In this way, an area of a force-exerted face of the tier control member can become large, and a biasing force of the biasing member and a release hydraulic pressure both can be large. A lock/release operation of the tier control member can be therefore performed with reliability to ensure the high stability of operation. Even if the tier control member is downsized without changing the biasing force of the biasing member, the area of force-exerted face of the tier control member can become large. It can ensure the high stability of operation without effect of the sliding resistance generated between the tier control member and the accommodation hole.
The first release hydraulic pressure chamber or the second release hydraulic pressure chamber may communicate with the advance side hydraulic pressure chamber at all times. In this way, when a hydraulic pressure of the advance side hydraulic pressure chamber is applied, the advance side hydraulic pressure chamber communicates with the release hydraulic pressure chamber, which does not communicate with the advance side hydraulic pressure chamber in ordinary cases. The release hydraulic pressure supplied from the advance side hydraulic pressure chamber can be easily supplied to both of the first and second release hydraulic pressure chambers, and the area of force-exerted face of the tier control member can be increased to ensure the high stability of operation.
It may further comprise a check valve supplying the higher hydraulic pressure of the advance and retardation side hydraulic pressure chambers to the tier control member as a release hydraulic pressure for releasing the lock of the tier control member, and at least one of the first and second release hydraulic pressure chambers may communicate with both the advance and retardation side hydraulic pressure chambers via the check valve. In this way, the check valve facilitates supplying the release hydraulic pressure supplied from the advance or retardation side hydraulic pressure chamber to both of the first and second release hydraulic pressure chambers. The area of force-exerted face of the tier control member can be increased to ensure the high stability of operation.
A force-exerted face of the tier control member accommodated in the second release hydraulic pressure chamber to which the release hydraulic pressure is supplied via the check valve may be a ring-shaped section defined at the end face of the rear major diameter section in the axial direction of the device. In this way, the release hydraulic pressure supplied from the advance or retardation side hydraulic pressure chamber can be subject to the tier control member with reliability to ensure the high stability of operation.
A force-exerted face of the tier control member accommodated in the first release hydraulic pressure chamber to which the release hydraulic pressure is supplied via the check valve may be a circular section of the front minor diameter section. In this way, the release hydraulic pressure supplied from the advance or retardation side hydraulic pressure chamber can be subject to the tier control member with reliability to ensure the high stability of operation.
An area of a force-exerted face of the tier control member, which is subject to a hydraulic pressure of the advance side hydraulic pressure chamber may be equal to or larger than an area of a force-exerted face of the tier control member, which is subject to a hydraulic pressure of the retardation side hydraulic pressure chamber. In this way, even if the release hydraulic pressure supplied from the advance side hydraulic pressure chamber is nearly equal to the release hydraulic pressure supplied from the retardation side hydraulic pressure, the lock of the tier control member can be reliably released against the biasing force of the biasing member.
It can therefore ensure the high stability of operation. Even if the lock of the tier control member is not quite released on application of the hydraulic pressure supplied from the retardation side hydraulic pressure chamber, a time for moving the tier control member back can be shortened on application of the hydraulic pressure supplied from the advance side hydraulic pressure chamber. When the relative rotation of the first and second rotors is started, the lock of the tier control member can be released in good timing.
It may further comprise a seal member arranged between the fitting hole and the retardation side hydraulic pressure chamber and creating a seal to block flow of actuating oil between the advance and retardation side hydraulic pressure chambers. In this way, the advance side hydraulic pressure chamber can communicate with both of the first and second release hydraulic pressure chambers, and the area of force-exerted face of the tier control member can therefore become large on application of the hydraulic pressure supplied from the advance side hydraulic pressure chamber. A biasing force of the biasing member and a release hydraulic pressure both can be large. A lock/release operation of the tier control member can be therefore performed with reliability to ensure the high stability of operation. Even if the tier control member is downsized without changing the biasing force of the biasing member, the area of force-exerted face of the tier control member can become large. It can ensure the high stability of operation without effect of the sliding resistance generated between the tier control member and the accommodation hole.
The fitting hole may be disposed at an approximately intermediate position apart from any of the maximum advanced side position and the maximum retarded side position, and a seal member may be arranged between the fitting hole and the retardation side hydraulic pressure chamber and creating a seal to block flow of actuating oil between the advance and retardation side hydraulic pressure chambers. In this way, the type of VVT locking the first and second rotors at the approximately intermediate position has the same effect as the other type of VVT. In brief, the advance side hydraulic pressure chamber can communicate with both of the first and second release hydraulic pressure chambers, and the area of force-exerted face of the tier control member can therefore become large on application of the hydraulic pressure supplied from the advance side hydraulic pressure chamber. A biasing force of the biasing member and a release hydraulic pressure both can be large. A lock/release operation of the tier control member can be therefore performed with reliability to ensure the high stability of operation.